Sadly it is not as straight forward as the A3 > A5 fold, firstly they are related in size A3 being 4 times the size of A5 and also you are only going to punch it to fit in one organiser not two... but I never baulk at a challenge.
So taking an A5 page and a Personal size page and comparing there size and the positioning of the holes it looks like this.
As you can see we have alignment with 5 out of the 6 holes but the A5 page will still be taller than the Personal page. If you repunch all 6 holes so that the two pages align at the top edge, you end up with an A5 page with 12 holes punched in it! This might be ok, but the page might be too weak if it is swapped in and out a lot.
An alternative is to punch one extra hole and then fold down the top 10mm and the bottom 28 mm and 54mm in on the right hand edge.
Another alternative is to fold the A5 page in half and then you are only aligning the 3 holes with the same spaced 3 holes in the Personal Filofax, this works, but you still have a slight over hang of about 10mm at the top of the page, which on my own organisers would be outside of the binder, so it would need to be folded down, and as above folded in on the right hand side to fit.
So yes it is possible to do, but there are potential issues of the folds and the resulting thickness of the folded page.